34 PLEISTOCENE MAMMALIA. 



is somewhat hexagonal in form. It is rather longer than wide, and is slightly longer than 

 the basi-sphenoid, to which it is firmly attached by a straight transverse suture. It forms 

 a strong plate of bone of nearly uniform thickness, articulated behind to the exoccipitals 

 in the whelp by a suture, of which the lateral portions are transverse. In the 

 median line, however, it sends back a square process, the free end of which is the lower 

 and anterior border of the foramen magnum. The lateral portions of this suture are 

 interrupted by the " foramen condyloide," which passes from the posterior edge of the 

 "foramen lacerum posterius" («) to the interior of the cranium near the anterior border 

 of the foramen magnum. This transmits the large motor hypoglossal nerve. The sides 

 of the bone are in contact M'ith rather than articulated to the tympanic, and above that 

 to the petrosal, the junction between them being interrupted posteriorly by the large 

 irregular "foramen lacerum posterius" (a) or "foramen jugulare " for the passage of the 

 eighth pair of nerves and a large vein connected with the internal jugular. The medullary 

 surface is somewhat concave, forming a lodgment for the " medulla oblongata." The 

 flatness of the lower surface is broken by two large rough depressions on each side close 

 to the tympanies for the insertion of the " recti antici majores " of the head, which take 

 their rise in several roots on the pleurapophyses of the cervical vertebrae. Immediately 

 behind them are the smoother but larger impressions of the "recti antici minores," which 

 have their origin in the " atlas." These impressions are represented in PI. VIII, in front 

 of the " foramen lacerum posterius." In the median line we sometimes find in Lion the 

 commencement of the tubercle for the attachment of the " constrictor pharyngis superior," 

 which is, however, mainly attached to the basi-sphenoid. This does not occur, as far as 

 we know, in Feiis spelcea. With the exception, perhaps, of a slight tendency to greater 

 width in the spelaean as compared with the leonine and tigrinc basi-occipitals, there is no 

 difference worthy of note. 



% 3. Exoccipitals and Supra-occipitals. (Pis. VI, VII, VIII, IX, X. Nos. 2, 3, 4). — 

 It is more convenient for purposes of description to treat these as one bone rather than in 

 accordance Avith their centres of ossification, because they are never found separate except 

 in the very youngest individuals, and because, firmly anchylosed together, they form the 

 main surface of connection between the head and the trunk. They compose a strong 

 plate of bone, triangular in outline, firmly articulated to the basi-occipital (PI. VIII, No. 1) 

 at right angles, and with it circumscribing the foramen magnum (Pis. VIII, IX). 

 On either side of the latter are two short thick pedicles of bone which point downwards 

 and backwards, and support the condyles by which the head is articulated to the atlas. 

 These point in their upper portion upwards, in the middle backwards, and in the lower 

 downwards. Their edges project over the sides of the pedicle, forming a fossa, which is 

 called the " condylian fossa " {h, Pis. VI and X). These are the portions termed by 

 Professor Owen the exoccipitals (No. 2). 



The two inferior angles of the bone are composed of the paroccipitals, or paramastoids, 



