THE OSSEOUS SYSTEM. 



307 



vertebra?, with cartilaginous processes, and with intervertebral ligaments. 

 2. Cartilaginous ribs, and a cartilaginous, entire sternum. 3. Wholly 

 cartilaginous extremities, with as many and similarly formed pieces as 

 there are afterwards bones, with the sole exception of the pelvic carti- 

 lages, which constitute a single mass. 4. And lastly, an incomplete 

 cartilaginous cranium. This primordial cranium, as it is termed 

 ("Mikrosk. Anat.," tab. iii. figs. 1-3), forms originally a continuous 

 cartilaginous substance, which corresponds, for the greater part, with 

 the occipital bone (except the upper half of the expanded portion), the 

 sphenoid (except the lamina externa of the pterygoid process), the mas- 

 toid and petrous portions of the temporal bone, the ethmoid, the inferior 

 turbinated bones, the ossicula auditus and the hyoid bone ; but it 

 also presents some cartilaginous portions, which never become ossified, 

 either remaining in the cartilaginous conditions during life, or afterwards 

 disappearing; as for instance, Meckel's process, two cartilaginous la- 

 mellae below the nasal bones, a narrow cartilaginous band connecting the 

 styloid process with the os hyoides, and two others, one of which extends 

 from the outer part of the ala parva laterally to the lamina cribrosa, 

 whilst the other stretches upwards and forwards from the cartilaginous, 

 mastoid, and petrous portions of the temporal bone. Consequently, in 

 the cartilaginous cranium of man, the vault of the skull is totally want- 

 ing, and almost all the lateral portions, as well as nearly all of what 

 afterwards becomes the facial bones ; nevertheless, at all events in the 

 true cranium, the parts not formed of cartilage are closed by a fibrous 

 membrane, representing in fact the further development of the soft, pri- 

 mordial, cranial capsule, so that the cranium at this time, though only in 

 part cartilaginous, is yet fully as complete as at an earlier period, and 

 always corresponds to its original soft rudimental form. In other Mam- 

 malia, as for instance, in the Pig, the cranium is much more completely 

 cartilaginous ("Microskop. Anatomy," tab. iii. figs. 4, 5). 



The complete development of the primordial cartilage, considered 

 liistologieally, has not yet been accurately traced in all its stages, either in 

 man or in mammalia. If we wish, therefore, to obtain anything like a 

 sufficient idea of it, we must at present have recourse in a great measure 

 to the lower Yertebrata. If the cartilage of the spinal column and of 

 the head be examined in the batrachian larva, it is readily seen, that 

 they are invariably constituted, while still in the soft state, of the same 

 formative cells with vitelline corpuscles, as all the other organs. Before 

 the development of the external branchiae, these cartilage-cells present 

 the form of closely approximated spherical cells, 0*007 to 0*009 of a line 

 in size, with nuclei measuring 0-0045-0-006 of a line, and filled with the 

 well-known vitelline corpuscles ; afterwards, when the branchiae have 

 made their appearance, the granular contents of the cells begin to dis- 

 appear, from within to without, whilst the nuclei become more distinct, 



