AET. 15 ANATOMY OF THE EARED AND EARLESS SEALS HOWELL 13 



only impossible to explain the dental differences between the two 

 families at the present time but in the absence of ancestral remains it 

 is unsafe to theorize on the probable development of the tooth pat- 

 terns. The dental arch is different in the two families, being narrow 

 in the Zalophus^ with alveoli almost parallel, while these diverge to 

 a greater extent in phocids, with Stenorhynchus occupying an inter- 

 mediate position in this as in so many other respects. The palatal 

 region is narrow in Zalophus and broad in the Phoca, while the 

 hamular processes are located far caudad in the former of their 

 position in the latter animal. 



In classifications of the Pinnipedia attention is usually called to 

 the presence in otariids and the absence in phocids of the alisphenoid 

 canal, mediad of the glenoid fossa, for the passage of the external 

 carotid artery. This is a convenient character for classification but 

 is not necessarily a precise criterion, for in the skull of a fur seal 

 {Callorhinus alascanus, No. 237266 U.S.N.M.) this canal is present 

 upon the left side but absent on the right. In Zalophus the foramen 

 rotundum (for the maxillary nerve) is just craniad of this canal, 

 and in the Phoca, mediad to the anterior part of the glenoid fossa. 

 Xext caudad is the foramen ovale (for the mandibular nerve), and 

 near this, the Eustachian canal. The apparent position of the stylo- 

 mastoid foramen (for the facial nerve) differs in the two animals, but 

 in both it is located as usual between the audital bulla and the mas- 

 toid. Ventrad of the basioccipital level upon the medial side of the 

 bulla in the Phoca is the carotid canal (for the external carotid 

 artery) and the direction of this is latero-dorsad. In the Zalophus 

 this foramen is mostly dorsad of the lateral margin of the basioc- 

 cipital, and its direction is directly craniad. A probe introduced 

 from the caudal end emerges into sight next to the Eustachian canal. 

 The jugular, or posterior lacerated foramen is next caudad, this 

 being a large fenestration in both, but somewhat more extensive in the 

 Phoca. Between this and the condyle is the condyloid foramen (for 

 the hypoglossal nerve), larger in the Zalophus^ but this difference is 

 not found to be uniform in the other pinnipeds. 



The pterygoid fossa is much broader in Phoca hispida than in 

 Zalophus but the significance of this is not readily interpreted. The 

 irregularity of the surface of the basioccipital in the latter indicates 

 stronger anterior rectus capitis muscles in this animal. In this as in 

 certain other species of phocids (as Cystophora) there is a large 

 medial vacuity in the basioccipital, which seems never to occur in 

 otariids. In all eared seals apparently the occipital condyles are 

 relatively narrow, while in the Phocidae they are much more flaring, 

 this being especially pronounced in Phoca hispida. The reason for 

 this is evidently that the articulation of the head with the neck has 



