THE SYSTEMATIC ANATOMY OF A FCETAL SEA-LEOPARD. 451 



with two intervening depressions, and represents the olfactory region of the 

 nasal fossa. 



(/t) The large maxillo-turbinal rudiment (m.r. t.), presenting upon its mesial 

 surface a number of narrow lamellae with intervening sulci : it is carti- 

 laginous and is covered by a mucous membrane lined by ciliated epithe- 

 lium. Anteriorly the maxillo-turbinal bone is attached to the outer wall 

 of the fossa, whilst posteriorly it fuses by an elongated pedicle with the 

 periosteum of the base of the skull. 



The buccal cavity is lined by a mucous membrane covered by stratified epithelium 

 with but few cell-layers. At the present stage of development, the membrane bones 

 of the cranial vault are partially ossified, but the bones of the base of the skull (basi- 

 sphenoid, basi-occipital) are still partly cartilaginous ; the sphenoid bone (see text-fig. 

 3, b) is in the " irruption "-stage of endochondral ossification, the process being seem- 

 ingly delayed by tin- rather late persistence of tin 1 , epithelial connection between the 

 hypophysis cerebri and the buccal epithelium.* 



The brain. General superficial anatomy (PI. II. figs. 1 and 2). The brain of 

 the present specimen shows some very well-defined characters, and on the whole 

 may be said to conform to the mammalian type : viewed from the dorsal aspect 

 (PI. II. fig. l), the following features are obvious : 



(i.) The large cerebral hemispheres separated by the longitudinal sulcus in which 



the falx cerebri is normally lodged, 

 (ii.) Behind the hemispheres, the crura cerebri and region of the mesencephalon, 



covered by fragments of torn pia mater, 

 (iii.) The cerebellum, consisting of the mesially situated rudiment of the vermis, 



and on either side of this the cerebellar hemisphere : the latter already 



present a number of flattened laminae with intervening sulci. 

 (iv.) The 4th ventricle in its lower half, with the restiform bodies bounding it 



on either side ; the floor of the ventricle is seen owing to previous removal 



of the roof of pia mater. 



The surface of each cerebral hemisphere is quite smooth upon its superior aspect, 

 and shows no indications as yet of any convolutions. 



Viewed from the side, several additional features become apparent, viz. (PI. II. 

 fig. 2) :- 



(v.) The olfactory lobe, and its connection with the ventral part of the fore-brain. 



(vi.) A wide shallow depression passing from the lower aspect of the fore-brain 

 upwards and backwards towards the hind-brain (future occipital lobe) : 

 this depression indicates the position of the future Sylviau fissure (PI. II. 

 fig. 2 2 ), and ventral to its posterior extremity a forward extension of the 

 hemisphere represents the rudimentary temporo-sphenoidal lobe. 



* See also P. T. HERRING on " Development of Mammalian Pituitary Body," Jaunt. Exjier. Physiol., 1909. 



(ROY. soc. EDIN. TRANS., VOL. L., 229.) 



