the corpora bigemina of Mammals, and the optic thalami; the dorsal roof forms the epiphysis or pineal gland, the corpus callosum and the anterior commissure, both of which consist of bundles of white nerve fibres and connect the right with the left hemisphere. The ventral portion of the hemispheres consists of the corpora striata, which are masses of grey brain-substance, and of the olfactory lobes, which mark the anterior end of the brain.

The central canal, which runs through the spinal cord, is continued into the brain, and forms the fourth ventricle in the hindbrain, extending dorsally into the cerebellum; and is then continued as "aquæductus Sylvii" through the midbrain, with lateral extensions into the optic lobes. The dilatation of this canal in the thalamencephalon is the third ventricle: it extends ventrally towards the hypophysis as the infundibulum, in a similar way

dorsally towards the epiphysis, and communicates through the foramen of Monro with the second and first ventricles; these being the cavities of the two hemispheres.

The hypophysis cerebri or pituitary body is lodged in the "sella turcica," a niche or recess formed by the anterior and posterior basisphenoid bones. This peculiar body is probably the degenerated remnant of a special sense-organ in the mouth of early Vertebrata, it being developed partly as an outgrowth from the roof of the mouth which fuses with a corresponding growth from the brain and then loses its connexion with the mouth.

The epiphysis cerebri or pineal body is the remnant of a sense-organ, possibly visual, as it is still functional in many Lizards possessing a lens, a retina-like accumulation of black pigment and a nerve, but quite degenerated in all Birds and Mammals.

The cerebellum of Birds is homologous only with the "worm" or middle portion of the cerebellum of Mammals, the lateral lobes being absent, although a pair of flocculi are present. Externally it exhibits a number of transverse furrows, which divide it into

lamellæ. On a vertically longitudinal, or "sagittal," section, it has a beautiful tree-like appearance. From the walls of the central cavity branch-like

white medullary fibres spread out, surrounded by a layer of reddish ganglionic cells, fol

lowed by larger ganglia (Purkinje's layer), and externally covered by a grey mantle of smaller ganglionic cells. Such a thin section, especially when stained with carmine, forms a fascinating object for the microscope, and is easily made.

The surface of the cerebral hemispheres in Birds exhibits no convolutions or gyrations as in the higher Mammals. In the Ratitæ and in many Passeres the surface is entirely smooth, but in Swimmers, Waders, Pigeons, Fowls, and Birdsof-Prey, there is a very slight furrow which might be compared with the Sylvian fissure.

(After A. Meckel.)

I-XII, the twelve pairs of cranial nerves; Ch. Chiasma of the

optic nerves cut across; Fl. Flocculus; H. Hypophysis; L.o. Optic lobe; Lg. Laqueus; F.S. Sylvian fissure; Sp. I. First spinal

nerve.

There is also very little grey substance in the surface layers of the hemispheres. Various attempts have been made, by Tiedemann,1 Serres,2 Leuret, and Bumm, to compare the weight of the whole brain with that of the body, or

1 Anatomie und Naturgeschichte der Vögel. Heidelberg: 1810.

2 Anatomic comparée du cerveau. Paris: 1824.

3 Anatomie comparée du système nerveux. Paris: 1839-57.

4

Das Grosshirn der Vögel. Zeitschr. für wissensch. Zool. xxxviii. (1883)

pp. 430-466, tabb. xxiv. -xxv.

the weight of the hemispheres with that of other parts of the central nervous system, in order to draw conclusions as to the intelligence of various Birds. When Birds are arranged according to the preponderance of the hemispheres over the rest of the brain, the first place is taken by the Passeres and Parrots (2·7 or 2.0 to 1), then follow Geese, Ducks, Waders, and Birds-of-Prey, lastly Fowls and Pigeons, the proportions in the Common Domestic Pigeon being 0.95 to 1, i.c. the forebrain weighs less than the rest, while in many Oscines it weighs nearly three times as much. The attempts to sort Birds according to the proportion of brain to body have led to no practical results, chiefly because the variable conditions of fat and lean subjects have not been considered. The absolute weight or mass alone of the brain is not a safe guide.

These

There are twelve pairs of cranial or brain-nerves which arise from the brain and leave the cranium through special holes. pairs, as in other Classes of Vertebrates, are frequently spoken of by their number, counting from the nasal region backwards to the occiput.

I. N. olfactorius forms the anterior and ventral continuation of the hemisphere of its side, but arises in reality from ganglionic cells in the thalamencephalon and the midbrain. It leaves the cranial cavity through a canal in the dorsal and median part of the orbit and ends in the ganglionic cells of the olfactory membrane of the nose.

II. N. opticus arises from the ganglionic cells of the mantle of the optic lobes. Immediately in front of the hypophysis is the optic chiasma, produced by the complete crossing of the fibres which compose the two optic nerves, those from the right optic lobe passing over the left, and those from the left lobe to the right side. From the chiasma start the right and left optic nerves, each leaving the cranium by the large optic foramen between the orbitosphenoid and alisphenoid, entering the orbit near the posterior and ventral corner of the orbital septum and ultimately forming the retina of the eye.

III. N. oculomotorius arises close behind the hypophysis, near the medio-ventral line, from the midbrain, enters the orbit behind or together with the optic nerve (II), and supplies most of the external muscles of the eye, namely the m. rectus superior, inferior, internus, and obliquus inferior. A ciliary, partly sympathetic, branch supplies the eyeball and the internal muscles (see EYE).

IV. N. trochlearis or patheticus is the only one which leaves the brain on its dorsal surface, namely as a thin thread winding its way from the midbrain upwards between the cerebellum and the optic lobes, and entering the orbit through a fine opening close to the optic nerve (II) in order to supply the m. obliquus superior of the eyeball.

V. N. trigeminus is next to the optic the thickest nerve, and of a complex nature, being motory and sensory. It arises from the sides of the mid- and hindbrain, forms the large Gasserian ganglion in the wall of the cranium, and leaves the latter in the form of three branches. The first or ophthalmic branch comes directly out of the ganglion through a foramen behind the optic (II), runs along the dorsal corner of the orbital septum, and leaves the orbit at its inner anterior corner in order to supply the palate, the bill, forehead, and the lacrymal gland. It is chiefly sensory, and consequently strongest in birds with tactile bills, like Ducks and Snipes. The second or upper maxillary branch runs along the ventral edge of the orbital septum, and besides the palatine and maxillary regions supplies the eyelids and Harder's gland. The third or inferior maxillary branch is the strongest of the three; it leaves the cranium together with the second through a foramen between the basi-alisphenoid and petrosal bones and innervates all the masticatory muscles, the parotid gland, and the whole of the under jaw.

VI. N. abducens is a very thin nerve arising from the hindbrain near the medio-ventral line, entering the orbit through a special foramen latero-ventrally from the optic foramen, and supplying the m. rectus externus and the two muscles of the nictitating membrane. It is entirely motory.

VII. N. facialis arises from the side of the hindbrain, possesses a ganglion (g. geniculatum), passes through the petrosal bone into the Fallopian canal, and sends the sympathetic sphenopalatine branch to the second branch of the trigeminal nerve (V). The facial nerve leaves the tympanic cavity behind the quadrate bone, supplies the digastric muscle or depressor of the mandible, the little stapedius muscle of the ear-bones, the mylo- and stylohyoid muscles of the tongue, and further on connects itself with branches from the first four cervical nerves and occasionally with branches from the glossopharyngeal nerve (IX), ultimately supplying the skin on the front of the neck. There are no branches, as in Mammals, to supply the face, nor is there in Birds a chorda tympani, i.e. a branch of the facial nerve joining the mandibular branch of the trigeminal nerve (V).

VIII. N. acusticus arises dorsally from the facial nerve (VII), of which it is the sensory portion. It is very short and thick, possesses a little ganglion, and spreads out in the cochlea of the EAR as the nerve of hearing.

IX. N. glossopharyngeus takes its origin from the dorso-lateral sides of the medulla oblongata, near the rhomboid fossa. It leaves the cranium through the foramen jugulare, which lies between the petrosal and the lateral occipital bones, and also serves as exit for the vagus nerve (X) and the jugular vein. Here the ninth nerve forms a big swelling, the ganglion jugulare, and is connected with the

ganglion of the vagus and with the large sympathetic g. cervicale supremum, receiving a strong branch from the stem of the vagus, and dividing into two branches :-One, the pharyngeal branch, supplying the upper portion of the pharynx and the gustatory papillæ of the palate; the other, or lingual branch, supplying the glottis, larynx, and the tongue, and acting chiefly as the nerve of taste.

X. N. vagus or pneumogastricus arises behind the glossopharyngeal (IX), and passes likewise through the jugular foramen. Its ganglion is connected with that of the glossopharyngeal and with that of the sympathetic system. The stem of this nerve receives a branch from the hypoglossal (XII) and takes up the accessory (XI). It runs down the side of the œsophagus, enters the thoracic cavity between the brachial nerve plexus and the carotid artery, then passes between the bronchus and the subclavian artery to the ventral side of the proventriculus, and joining its fellow from the other side, spreads out to supply the stomach. Other branches leave the principal stem of each vagus at the level of the bronchi to supply the liver, heart, and lungs, and as the recurrent laryngeal branch also supply the distal portion of the trachea and oesophagus. Some fibres of the vagus often extend beyond the stomach, and are connected with the sympathetic nerves of the trunk, supplying part of the intestinal canal.

XI. N. accessorius, a little nerve taking its origin between the dorsal and ventral roots of the third cervical nerve, runs upwards through the occipital foramen into the cranium, and joins the ganglion of the vagus (X), to leave the cranium with the latter and to supply the cucullaris muscle or constrictor colli.

XII. N. hypoglossus arises ventro-laterally from the medulla oblongata, and leaves the cranium by two foramina in the lateral occipital bone, in front of and sidewards from the occipital condyle. It supplies the m. complexus, forms a connecting loop with the first cervical nerve, innervates some of the cervical muscles, and divides into two branches-one of which supplies most of the muscles of the tongue and communicates with its fellow on the undersurface of the tongue, while the other innervates the muscles of the larynx, and then descends along the side of the trachea to the syrinx in order to supply the vocal muscles and membranes.

BRAMBLE-FINCH or BRAMBLING (Germ. Brämling), names of one of the most beautiful of our annual visitors, Fringilla montifringilla, which has its home in the birch-forests of Northern Europe and Asia, whence it yearly proceeds, often in flocks of thousands, to pass the winter in more southern countries. It is congeneric with the CHAFFINCH, but is still more brightly coloured, especially in summer, when the brown edges of the feathers being shed, it presents a rich combination of black, white, and orange.