Royal Society. 239 



5 sacral, and 18 caudal vertebrae. The first to the fifth dorsal ver- 

 tebrae are characterized by having the ordinary number of articular 

 processes (zygapophyses), two before and two behind ; and by 

 having three articular surfaces for the ribs on each side, one on the 

 centrum, one on the neurapophysis, and one on the diapophysis. 

 The sixth dorsal vertebra has an accessory zygapophysis between 

 the posterior pair ; the thirteenth dorsal has one between the anterior 

 pair ; the seventh to the twelfth inclusive have the accessory median 

 zygapophysis between both the anterior and posterior pairs of the 

 ordinary zygapophyses. The fourteenth and succeeding dorsals 

 have no costal surface on the diapophysis or centrum. The fif- 

 teenth has both metapophysis and anapophysis — the latter with an 

 articular surface : the sixteenth superadds the parapophysis with an 

 articular facet. 



The lumbar vertebrae lose the costal surface on the centrum, and 

 retain the metapophyses, anapophyses and parapophyses. The 

 nature of these accessory processes was explained by reference to 

 the descriptions and figures of the exogenous processes of vertebrae 

 in Part I. of the present Memoir. 



The characteristics of the cervical vertebrae were next detailed. 

 Of the five anchylosed sacral vertebrae, three are confluent with 

 the iliac bones, and two with the ischia. 



The fourteen anterior caudals are characterized by articular sur- 

 faces for haemapophyses. These elements are separate from each 

 other in the first caudal, and confluent as usual at their distal ends, 

 forming a ' chevron-bone' in the others. The posterior zygapophy- 

 ses lose their articular surfaces in the eleventh caudal ; the anterior 

 ones disappear in the twelfth : the metapophyses have subsided in 

 the fifteenth. The neural canal is unclosed above in the sixteenth ; 

 and the vertebra is reduced to its central element in the last two 

 caudals. 



The skull is remarkable for its small proportional size, for its long 

 and slender cranial portion, its large and complex zygomatic arches, 

 its broad truncate facial part, with the slender produced premax- 

 illaries, and for the great depth of the middle of the lower jaw. 



The mastoid element developes a large tuberous process and a 

 deep semicircular articular cavity for the stylohyal. The malar 

 bone sends down a long process outside the lower jaw. The num- 

 ber of teeth is ^^=18, the fifth in the upper jaw being the smallest. 

 They are alike in structure, and differ but little in shape: thegrinding 

 surface in most is crossed by two transverse ridges ; the summits of 

 which are formed by hard dentine ; the rest of the tooth being 

 composed of a central body of vaso-dentine and a peripheral mass 

 of vascular cement. The microscopic characters of these several 

 constituents of the teeth were then described. Each tooth is deeply 

 implanted in the jaw^, where it terminates without dividing into 

 fangs, by a widely open pulp-cavity for a persistent matrix, ensuring 

 perpetual growth. The stylohyal bone has the form of a hammer, 

 with a long, slightly bent handle ; one part of the head being thick- 

 ened and rounded for articulation with the cavity in the mastoid. 

 The scapula presents almost the form of a trapezium, with the 



