DR. J. MUEIE ON THE ANATOMY OF THE SEA-LION. 505 



median line, is the very great horseshoe-shaped jugular vacuity. At its fore border, 

 partially hidden within the bone, is the entrance of the carotid canal, which pursues a 

 course through the tympanic, opening, as aforesaid, at the lacerum medium. A shelf 

 of bone divides the postcarotic foramen from the deeper-placed aquseductus cochleae. 

 Lastly, to the rear, and a trifle within the jugular fossa, is the basal opening of the 

 anterior condyloid foramen. 



e. Interior of the Skull. — As regards peculiarities in the form of this cavity, allusions 

 will be found under the description of the encephalon ; here I confine my remarks to the 

 osseous superficies and foramina. Laterally the walls of the calvarium are exceedingly 

 thin — anteriorly, or in the frontal region, excessively thick and cancellous — occipitally 

 equally porous but very moderate in thickness, and with capacious venous channels. 

 The bony tentorial plate, necessarily broken on removal of the vertex, as displayed in 

 fig. 10, is uneven, and pitted with minute and larger-sized foramina. The anfractuosi- 

 ties of the canopy of the skull, and the irregular cerebral-pitting depressions are most 

 unusually well marked ; and, moreover, innumerable minute and larger-sized foramina 

 bear evidence of the great vascularity of the osseous structure. The longitudinal venous 

 groove is very deep and well pronounced ; and so are the furrows lodging the meningeal 

 arteries &c. 



The floor of the cavity (somewhat bluntly boat-shaped) possesses numerous irregu- 

 larities and vacuities ; but the orbi to-frontal parietes are smoother and incline to the 

 perpendicular. The olfactory fossae are narrow, high, and deep, the cribriform plates of 

 the ethmoid assuming the vertical, with a retroverted spinous partition. Immediately 

 behind the latter is a single low-arched perforation for the optic nerves, each nerve 

 escaping into the back of the orbit through the orbito-sphenoid bone, the perforation 

 drilling the median wall (fig. 5). Along the solid mid-basilar plane, successively from 

 before backwards, the noteworthy points are: — adjoining the optic arch a transverse 

 cleft, through non-ossification of praesphenoid suture ; a full broadish processus olivarius, 

 comparatively deficient in mid clinoid processes ; a deeply excavated sella turcica, whose 

 bayed front margin carries relatively large angular postclinoid processes ; a scooped basi- 

 sphenoid lodging the pons Varolii ; to the rear of this, in the basioccipital, a great lop- 

 sided hollow (possibly a vascular recess), chiefly to the left, though shown on the right 

 in the reversed fig. 9. 



At the sides defined areas correspond to the orbito-parietal and temporal lobes of the 

 cerebrum, whilst that which receives the cerebellum and lateral sinuses is markedly 

 characterized by its depth, prominent nodular periotic, and large jugular orifice. 



Of other fissures and visible foramina, that agreeing with the lacerum anterius extends 

 half an inch antero-posteriorly, an outer eaved bony plate partly overriding it ; a groove 

 about another half inch leads back and outwards to a large foramen ovale, these and an 

 inner adjoining space (in the fresh subject) being occupied by the Casserian ganglion and 

 fifth-nerve divisions. What apparently answers to the lacerum medium (giving ingress 

 to the internal carotid artery) and the foramen spinosum is a widish perforation and 



