340 CHARLES CLIFFORD MACKLIN 



The ventral part of the lower border has been described as the 

 neural arch. Dorsal to this the character of the border changes 

 completely, for, after the dorsal foraminal prominence is passed 

 it loses its thickness and roundness on section, and becomes thin 

 and serrated. This portion borders the superior occipital incis- 

 ure, and really represents the lower portion of the original dorsal 

 border, the upper portion being united to form the tectum pos- 

 terius. The latter, according to Levi's investigations, is formed 

 somewhere between the 14 and 17 mm. stages by dorsal fusion 

 of the squamae. 



The surface outlined by the above-described boundaries has 

 been seen to become narrower ventrally in the lamina alaris 

 (fig. 5). This is a wing-like plate of cartilage, bounded ventrally 

 by the processus paracondyloideus. The outer edge of its up- 

 per surface bears the caudal extremity of the pars canalicularis 

 of the otic capsule, and medial to this the upper surface, which 

 looks principally cranially, particijiates ventrally in the structure 

 of the hollow recessus jugularis, and forms the floor of* the re- 

 cessus supraalaris. The latter is a cleft between the lamina 

 and the overhanging pars canalicularis of the otic capsule (fig. 5) 

 through the lateral part of which the transverse sinus passes. 

 The lower surface of the lamina alaris is also hollowed in the 

 more central parts of the paraforaminal area (fig. 2, p. 372), and 

 the plate is, therefore, quite thin — in fact on the right side it is 

 perforated by a minute foramen, just lateral to the neural arch 

 (fig. 1), and posterior to the jugular tubercle, through which a 

 small vein passes. This foramen is doubtless the representative 

 of the condylar foramen of the adult condition. Dorsally the 

 lamina alaris becomes wider, thicker, and more vertical in slope, 

 as it passes into the larger posterior portion of the squama. 

 The inner surface is smooth, and presents, dorso-lateTal to the 

 tip of the superior occipital incisure a small oval foramen on the 

 right side, but not on the left, through which»a small vein passes 

 (fig. 1). A very shallow groove runs parallel to the neural arch, 

 just lateral to its upper aspect. 



Upon the outer surface the most prominent object is a rounded 

 eminence, — the lateral occipital eminence — (fig. 3) which appears 



