288 MR PHILIP J. WHITE ON THE 



pneumogastric nerves. Owing to the oblique direction of these canals from within 

 outwards and backwards, the region is marked out somewhat in the form of a V. The 

 apex of this V is directed forwards, and its short backwardly-directed limbs receive the 

 anterior portion of the first vertebra between them. The fore part of this vertebra, save 

 at a point (Fig. 5, S3) on either side of its arch, is in contact with the occipital region. 

 Mesially, its centrum (Figs. 3 and 5, V") is continuous with the skull, but the lateral 

 portions of its centrum (Fig. 3, Vp), which present considerable expansions, are distinct 

 therefrom, although firmly bound to it by connective tissue. These lateral vertebral 

 expansions abut against the occipital processes (Op), which are thrown outwards 

 and backwards from the occipital region. The surfaces of the vertebral expansions and 

 occipital processes where they meet each other are smooth. Again, the anterior portion 

 of the arch of the first vertebra (Fig. 5, V) lies within the occipital foramen, and is in 

 contact with its upper and lateral margins. A canal (Fig. 5, S3) for the transmission of 

 the third spinal nerve lies on either side between the skull and the middle portion of the 

 vertebral arch. The part of the arch below these canals rests on slanting surfaces on 

 the lower lateral edge of the foramen magnum, and the part above them enters more 

 freely within the foramen, and is overlapped by its dorso-lateral margin. In the smaller 

 skulls of Laemargus examined I find that the neural arch, although bound to the 

 margin of the foramen magnum by connective tissue, is distinct from it, and this con- 

 nection permits of a little movement in a vertical direction ; but in the largest skull 

 at my disposal I noticed a much more intimate connection between the arch of the first 

 vertebra and the skull. Especially is this the case with the portion of the arch below the 

 canals for the third spinal nerves, where the arch and skull are continuous with each other. 



In its cranio-vertebral connection Laeinargus presents affinities to Hexanchus and 

 such forms as Acanthias and Scymnus. In having the lower mesial portion of the first 

 vertebra continuous with the cranium, and in having an intimate relation between the 

 arch of this vertebra and the margin of the foramen magnum, Laemargus ranks with 

 Hexanchus ; in the connection of the expanded portions of the first vertebral centrum 

 with the occipital processes it agrees with Acanthias, Scymnus, &c. I find no joint 

 cavities existing between the lateral vertebral expansions and the occipital processes. 

 It appears that Gegenbaur finds such in Scymnus. 



The dorsal portion of the occipital region slopes backwards towards the vertebral 

 column, and at its hinder part is somewhat vertical. In a line with the spinous processes 

 of the vertebrae, and extending from the back of the parietal fossa (Figs. 1 and 5, P) on 

 the roof of the skull to the foramen magnum, is a crest, the occipital crest (Co), which 

 is most prominent about the middle of its extent. Its development in Laemargus 

 resembles that found in Acanthias and Centrophorus calceus, rather than that of 

 Hexanchus or Heptanchus, in the latter of which the crest attains its greatest develop- 

 ment among Selachians. 



The ventral portion of the occipital region is continuous with, and assists in forming 

 the hinder part of the large basilar plate (Fig. 3, Bp) of cartilage which constitutes 



