628 



SKELETON. 



and the neural arches (2). They are " exo- 

 genous." Now the thoracic rib (4 of A) is 

 also the true homologue of the lumbar mis- 

 named and mistaken " transverse" process 

 (4 of B), for both these structures are iden- 

 tical in every respect : 1st, they hold the same 

 serial order ; 2d, they are posited in the 

 same situation with respect to the other ver- 

 tebral elements ; 3d, they are autogenous ; 

 4th, the so called " transverse process " (4) 

 of the, lumbar vertebra (B) is that very struc- 

 ture which occasionally presents to us in arti- 

 cular costal form and function as seen in 

 4 of F, Jig. 444., thereby more closely be- 

 coming assimilated to the thoracic rib of the 

 dorsal vertebra ; 5th, by negative evidence 

 it may be shown that the thoracic rib (4 of A) 

 is the true homologue of the so named trans- 

 verse process (4) of the lumbar vertebra (B), 

 for while it stands manifest that the " tuber- 

 cle " (3) * of the latter is counterpart of the 

 transverse process (3) of the dorsal vertebra, 

 then it must follow that the thoracic rib and 

 the lumbar " transverse process " j" so called 

 are also counterparts. The lumbar vertebra 

 therefore produces the costal appendage.j 



PROP. VIII. All the lumbar vertebra develop 

 costal appendages. That which is true of 

 the first lumbar vertebra and the last costo- 

 vertehral thoracic form must be true of the five 

 lumbar vertebrae and the twelve thoracic costo- 

 vertebral forms, for all the lumbar vertebrae are 

 fashioned of an equal number of elementary 

 pieces. The difference which exists between 

 lumbar vertebrae and thoracic costo-vertebral 

 forms is one of quantity, and the costal ap- 

 pendages of both are those which show this 

 quantitative difference. The ribs of the 

 thorax are proportionably larger than those 

 of the loins. In the thorax the costae (4 of A, 

 j<7.447.) appear articularly connected with the 

 centrum (5). In the loins the costaj (4 of B, 

 Jig. 447.) are fixed or anchylosed to the ver- 

 tebral centrum (5); but this state of anchy- 

 losis is by no means constant ; and when they 

 articulate freely with the centra of the lumbar 



* The " tubercle " is, in human anatomy, ac- 

 counted as a process specially characterising the 

 lumbar vertebra as distinct from the dorsal vertebra, 

 in which latter the tubercle is supposed to have no 

 counterpart. 



f Cruveilhier states, as a peculiarity.of the lumbar 

 transverse process, that it sometimes remains arti- 

 cularly separate, and simulates the costal character, 

 becoming the " supernumerary rib." Meckel alludes 

 to the fact also. 



J On referring to the " Homologies of the Yerte- 

 brate Skeleton," I find the following affirmation : 

 " Each of the five succeeding segments is repre- 

 sented by the same elements (centrum and neural 

 arch) coalesced, that constitute the so called dorsal 

 vertebra ; they are called ' lumbar vertebra ; ' they 

 have no ossified pleurapophyses." Professor Owen's 

 " pleurapophysis " is the rib or costal appendage of 

 his typical vertebra. While he states, therefore, 

 that the lumbar vertebra has no pleurapophysis, he 

 means that it has no rib or costal piece. This over- 

 sight (which, with all respect, I believe it to be) 

 has arisen from the evident error of mistaking the 

 lumbar transverse process as being the counterpart 

 or homologue of the dorsal transverse process, which, 

 if such were, the case, would leave the lumbar ver- 

 tebra without a rib. 



vertebrae, then the elements (4) are as ribs 

 seen in ?,Jig. 444. 



PROP. IX. The sacral vertebra develop 

 costal appendages. If it can be demonstrated 

 that the first sacral vertebra is developed of 

 nuclei equal in number, and identical in situa- 

 tion, in form, and in mode of growth with those 

 which are proper to lumbar vertebrae, then we 

 may account both lumbar and sacral vertebrae 

 as homologous with the costo-vertebral tho- 

 racic form. And it does appear that the sa- 

 cral vertebra (v,J?g. 448.) is actually fashioned 



of the same number of elements. For the serial 

 order of nucleary deposition throughout the 

 whole length of the spinal axis proves that 

 the anterior nucleus (4) of the lateral mass 

 (3, 4) of the sacral vertebra (B) is the true 

 homologue of the so called " transverse pro- 

 cess " (4) of the lumbar vertebra (fi,/g. 447.), 

 and of the costa (4) of the thoracic form (A, 

 tfg.448.) and of the anterior half of the cervical 

 transverse process (4, Jig. 445.). All these 

 pieces hold serial order ; all are autogenous 

 growths ; all are posited in the same relation 

 with respect to the other vertebral pieces 

 (1, 2, 3, 5) of the cervical, dorsal, and lumbar 

 forms. Now, having once determined the 

 proper identity of the anterior nucleus (4) of 

 the lateral mass (3, 4) of the sacral vertebra 

 (P'fig* 448.), it becomes easy to recognise the 

 homological cast and relation of all the other 

 pieces of the sacral vertebra. The posterior 

 half (3) of the lateral mass of the sacral ver- 

 tebra (B) is the counterpart of the " tubercle " 

 (3) of the lumbar vertebra (B,^/zg.447.), of the 

 transverse process (3) of the dorsal vertebra 

 (A, Jig. 448.), and of the posterior half of the 

 transverse process (3) of the cervical vertebra 

 (Jig. 445.). The spinous process ( 1 ), laminae 

 (2, 2), centrum, or body (5) of the sacral 

 vertebra (B, Jig. 448.) are evidently identical 

 with the like- named parts of all the other 

 vertebrae correspondingly numbered. It will 

 hence appear that sacral vertebrae do not 

 differ from other vertebrae ; and that it is an 

 error as to the identity of the anterior nucleus 



