DE. J. MURIE ON THE FOEM AND STRUCTUEE OF THE MANATEE. 181 



drangular, but rounded at the corners ; and the crescentic cerebellar posterior margin 

 lengthens this behind. The breadth to the cerebral length is absolutely great, but less 

 than in the Delphinidse. In profile view the height of the cerebrum is nearly equal to 

 the length, and the figure, as a whole, remarkably Elephantine. The posterior cerebral 

 lobes cover but half of the cerebellum, thus leaving a considerable portion of the latter 

 free at the posterior end of the superior longitudinal fissure. 



Four lobes may be distinguished, viz. frontal, parietal, occipital, and temporal. The 

 frontal lobe (F) is remarkably deep and perpendicular in direction, but of considerably 

 less diameter antero-posteriorly. Its orbital division fills the anterior fossa of the 

 cranial cavity ; and its frontal part abuts against its anterior wall, the large olfactory 

 bulb being situated towards the lower end of the latter. The parietal lobe (P), as 

 defined by cerebral anatomists, may be said in Manatus to consist of two parts — to wit, 

 that anterior and that posterior to the deep transverse Sylvian fissure. The former is 

 a broad coronal band ; the latter is a markedly three-sided area, occupying chiefly the 

 vertex, but also partially the lateral surface of the brain, and appears to represent the 

 angular lobule of some authors. 



The occipital lobe {0) forms chiefly the rounded broad knuckle of the hinder surface 

 of the cerebrum, and is scooped out considerably below and mesially for the reception 

 of the cerebellum. The temporal (T), like the frontal lobe, is very deep, but of 

 smaller antero-posterior diameter than it, and not quite so perpendicular in its long 

 axis. In fact, it forms a thick, somewhat conical, mass which lies obliquely down- 

 wards and forwards, and occupies the wide sunken anterior area of the posterior fossa 

 of the skull's basis. 



The so-called central or median lobe, said to be of good size in the Elephant, I could 

 not differentiate in this Manatee, in consequence of the unsound condition of the 

 cerebral substance. Its existence, however, I cannot question. 



The cerebral mass, as a whole, is fair-sized, full, and with very convex surfaces in aU 

 directions. The hemispheres are divided by a deep, widish, great longitudinal fissure, 

 and each, moreover, possesses a most trenchant division into anterior and posterior half 

 by the Sylvian fissure. 



As regards parts at the base of the encephalon, the pituitary body, when fii'st 

 examined, appeared relatively large, was very vascular, flattish, and of a trefoil figure. 

 It occupied a greater area lengthwise and across than pi, figs. 33, 34, represent. The 

 transverse lozenge-shaped interpeduncular space, bounded by the optic tracts and crura 

 cerebri, is fair-sized. What appears as corpora albicantia, and possibly tubera cinerea, 

 are two antero-posterior, moderately large, oval eminences, situated in the middle of 

 the space, and behind and at the sides of these, respectively, distinct posterior and 

 anterior perforated spaces. Each crus {cr) is long, full, and prominent, and the two 

 diverge rather obliquely, not separating entirely till a short distance from the pons. 

 The pons Varolii [pv) is rather flat-surfaced, as, to a less degree, are the cerebral 



