474 SCHULTE, SEI WHALE. 



where they show important departures from adult conditions. For the study of the cartilaginous 

 structures deBurlet's fine studies of the chondrocranium have been of the greatest assistance, 

 and I am also under obligations to Prof. W. K. Gregory, who has allowed me to consult him upon 

 many points of difficulty. 



Norma occipitalis. As a whole this surface narrows towards the vertex from the post- 

 glenoid processes; this outline is however broken at the sides by the projection of the zygomatic 

 processes of the squamosal and, farther dorsad, by the rounded convexities of the parietals. 

 The foramen magnum is enclosed between the exoccipitals and basioccipital which are represented 

 by a continuous cartilage in which three ossification centres have appeared. Those of the 

 ex-occipitals are quadrangular and occupy the greater part of the intervals between the paroc- 

 cipital processes and the condyles. The third is much smaller and situated in the basioccipital. 

 The foramen magnum is oval with its long axis dorso ventral; it narrows ventrally between 

 the condyles and in its dorsal contour a similar but slighter narrowing is present. Vertically 

 it measures 10 mm., transversely 8 mm. The plane of its orifice looks caudad and to a slight 

 degree dorsad. The condyles are born on very short condylar processes. They are almost 

 flat transversely, moderately convex dorsoventrad. The lateral margins are strongly convex, 

 almost angulate at their region of greatest convexity where they pass on to the base of the 

 skull. The mesal borders are nearly straight except towards the extremities where they arch 

 laterad. These straight mesal margins converge until they are only 1.5 mm. apart. Between 

 them and the margin of the foramen magnum is a small area serving for the attachment of 

 ligaments and showing near its apex the section of the notocord. The condyles measure 13 mm. 

 in length, 7 mm. at their greatest breadth. The distance between their caudal extremities is 10 

 mm., between their ventral 4 mm. Lateral to the condyle is a narrow gutter in which is inserted 

 the combined scalenus and rectus anticus; beyond this the cartilage rises in blunt elevations. 

 Of these the most ventral is the paroccipital (paramastoid) process, which gives attachment 

 to the rectus capitis lateralis, and is placed dorsolateral to the jugular foramen. It is separated 

 by a depression from a more prominent vertical ridge, which gives attachment to an atlanto- 

 occipital muscle, the superior oblique. Dorsal to this, again separated by a concavity, is a broad 

 convexity serving for the attachment of the longissimus dorsi and of the muscle which I have 

 described as the trachelo-occipitalis. 



The supra-occipital is excluded from the foramen magnum by the exoccipitals. It is ob- 

 scurely pentagonal in form, the rostral and lateral margins tending to fall into an irregular 

 arch. In its whole extent it affords attachment to the semispinales muscles. Rostrad its margin 

 slightly overrides the interparietal and here gives origin to the occipitalis. Near its lateral 

 margin it is in contact with the parietal, between which and the interparietal is a broad mem- 

 branous area. 



Lateral to the exoccipital, between it and the parietal and squamosal, is a deep depression, 

 filled in the natural condition of the parts with dense connective tissue. On the removal of this, 

 the otic capsule is exposed presenting a surface concavo-convex dorsoventrad and rising almost to 

 the level of adjacent bones as it approaches the base of the skull, where it is joined by the hyoid 

 bar. Here the facial nerve emerges on the caudal aspect of the stylo-hyal. 



Ventral to the exoccipitals appears the auditory bulla, and in the angle between it and the 

 ex- and basi-occipital is the jugular foramen, which affords passage to the hypoglossal nerve in 

 addition to the ninth, tenth and eleventh, there being no condyloid foramen. The jugular 



