;6o GENERATION AND DEVELOPMENT. 



ossified portions exist in all the cervical vertebrse, and 

 gradually become so much developed in the lower part of 

 the cervical region as to form the upper false ribs of this 

 class of animals. The same parts exist in mammalia and 

 man ; those of the last cervical vertebrso are the most 

 developed, and in children may, for a considerable period, 

 be distinguished as a separate part on each side, like the 

 root or head of a rib. 



The true cranium is a prolongation of the vertebral 

 column, and is developed at a much earlier period than the 

 facial bones. Originally, it is formed of but one mass, a 

 cerebral capsule, the chorda dorsalis being continued into 

 its base, and ending there with a tapering point. This 

 relation of the chorda dorsalis to the basis of the cranium 

 is persistent through life in some fish, e.g., the sturgeon. 

 The first appearance of a solid support at the base of 

 the cranium observed by Miiller in fish, consists of two 

 elongated bands of cartilage, one on the right and the 

 other on the left side, which are connected with the car- 

 tilaginous capsule of the auditory apparatus, and united 

 with each other in an arched manner, anteriorly beneath 

 the anterior end of the cerebral capsule. Hence, in the 

 cranium, as in the spinal column, there are at first de- 

 veloped at the sides of the chorda dorsalis two symmetrical 

 elements, which subsequently coalesce, and may wholly 

 enclose the chorda.* 



Development of the-Face and Visceral Arches. 



It has been said before that at an early period of 

 development of the embryo, there grow up on the sides of 

 the primitive groove the so-called dorsal lamina, which at 



* For much new and original matter relating to the development of 

 the cranium, the reader is referred to the important lectures on Com- 

 parative Anatomy, delivered at the College of Surgeons by Professor 

 Huxley. 



