158 
ME. J. LOCKHART CLARKE ON THE STRUCTURE OE 
nucleated cells of every variety of shape, as represented in fig. 8, magnified 220 dia- 
meters. 
From the plexus on the inner side of the lobe the bundles converge and unite to form 
the fibrous portion of the peduncle (z, figs. 3 & 6). In fig. 3, which represents a longi- 
tudinal section of the lobe, they are seen to decussate in a very striking manner ; but in 
planes at right angles to it there is no appearance of decussation, as may be seen in 
fig. 6, which represents a transverse section through the middle of the lobe and peduncle 
in the direction of the line b fig. 2. Moreover, it may be here observed that the fibres 
occupy only the inferior half of the peduncle, the superior half (z 1 ) consisting chiefly of 
masses of nuclei and small cells like those of the lobe, and giving attachment to the 
tubercle (z") by a short and narrow pedicle or neck. This little body is pyriform, inclined 
somewhat outward, and composed of closely-aggregated nuclei connected with a multitude 
of fibres which converge to the neck and then spread through the cells of the peduncle. 
Having thus concluded my description of the optic lobes and their peduncles, I will 
offer a few brief remarks on the general structure and connexions of the remaining 
cerebral centres, with the view of determining their homologies. The foremost or 
bilobed pharyngeal ganglion in situ is rendered quadrangular by the roots of the nerves 
which it gives off. In front it gives off from each angle a thick nerve-trunk ( a , a), which 
soon divides into two branches. One of these is distributed on the outer side of the 
mouth to the powerful muscles which move the beak, while the other turns inward to 
the laminae or turbinated folds of the palate. These folds are muscular, but have a 
strong resemblance to the nasal laminae of fishes and other vertebrata, and are every- 
where lined with mucous membrane and epithelium*. Between the large nerves given 
off from the angles of the ganglion, numerous smaller branches proceed directly forward 
to different parts of the mouth. Some of them may be traced to the muscular bands 
that descend to the base of the spiniferous tongue, which is situated at the bottom and 
in front of the turbinated palate. The ganglion itself has a composite structure. A 
longitudinal section, that is, a section behind-forward, is oval or fusiform. Examined 
under a sufficiently high power, it is found to consist of two kinds of tissue — (1) a central, 
oval, and whitish nucleus ( i, fig. 9) composed of the closest interlacement or network of 
the finest nerve-fibres, with some intervening granules ; and (2) ,a surrounding grey layer 
of nucleated cells ( 2 , 2 ), in connexion with fibres proceeding from the central nucleus. 
Above, and especially below, the nucleus reaches nearly to the surface of the ganglion, 
so that at those parts the layer of nucleated cells is very thin; but in front ( 2 ) and 
behind ( 2 ') it is much deeper. From the distribution of its nerves to the muscles 
of the mouth and tongue, and to the turbinated laminae of the palate, this ganglion 
would seem to correspond to the centres of the fifth, the ninth or hypoglossal, and 
perhaps the olfactory and gustatory nerves of vertebrated animals. 
The second and larger ganglion ( c c, fig. 1), which is connected with the former by two 
* They communicate with the mouth by openings or fissures in the palate, and appear to he the olfactory 
organs. 
