754 



ANATOMY OF VERTEBRATES. 



ascending ramus of the mandible, and a smooth joint-like sur- 

 face, fitting into the upper concavity of the inverted angle, 

 answering to the persistent inner articular part of the condyle in 

 birds. 1 The fourth hsemal arch is close to the occiput in the Rumi- 

 nant, and retrogrades as the neck is lengthened out by vertebra 

 interposed between head and chest. It retains, in Cetaceans, 

 almost the typical position exemplified in Fishes. 



The common ossification of articular ends of bones from centres 

 distinct from that of the shaft is a mammalian developmental cha- 

 racteristic. The ultimate confluence of the 6 epiphyses' (vol. ii. 

 p. 297) with the f diaphysis ' indicates maturity of growth : but 

 in this relation there are differences in the same skeleton and in 

 different species. In Man the epiphyses of the limb-bones toward 

 which the ' arterial nutritiae ' run (p. 619) first coalesce with the 

 shaft ; those at the distal end of the humerus and proximal ends 

 of the two antibrachials, e. g., at puberty, those at the opposite 

 ends of the same bones at the twentieth year. The proximal 

 epiphysis of the femur coalesces about the eighteenth year, the 

 distal one at the twentieth ; the proximal epiphysis of the tibia 

 joins the shaft about the twenty-fifth year, the distal epiphysis 

 five years earlier. The epiphyses of the vertebral bodies coalesce 

 about the twenty-first year in Bimana, but they continue distinct 

 for a much longer proportional period of life in Cetacea. Epi- 

 physes and short bones of limbs, those of the carpus and tarsus, 

 e. g., continue cartilaginous some time after the shafts of the 

 long bones are ossified, as shown in fig. 586. This figure also 

 exemplifies the early manifestation of ordinal characters; the 

 inner digit of the pelvic limb, in the foetal Monkey ( Cercopithecus 



sabceus) already shows by its relative 

 shortness and divergence from the 

 others that it is destined to oppose 

 them, and to terminate the member by 

 a prehensile hand: while, from the 

 earliest manifestation of the digits of 

 the same limb in the human embryo, 

 the ( hallux ' by its proportions and 

 parallelism with the other toes indi- 

 cates the destination of the answerable 

 part to become a plantigrade foot, perfected to sustain and move 

 the body of an erect Biped. 



§ 409. Membrana pupillaris. — The differences in degree of indi- 



586 



From foetal lower limb ; nat. size. 

 a. Monkey. 6, Man. cclxxvii". 



1 ccxcv". p. 727. 



