552 



ON THE THEORY OF THE VERTEBRATE SKULL 



converts it, anteriorly, into the palatine, and posteriorly, into the 

 pterygoid bone. The mandibular cartilage itself becomes divided into 

 two portions, a short, proximal, and a long, distal, by an articulation 

 which makes its appearance just below the junction of the pterygo- 

 palatine cartilage. The long distal division is termed, from the name 

 of its original discoverer, Meckel's cartilage. It lengthens, and an 

 ossiiic deposit takes place around, but, at first, not in it. The 

 proximal division in the mammal ossifies, but usually loses its con- 

 nexion with the pterygoid, remains very small and becomes the 



Fig. 4. — Dissection of the cranium and face of a Fcetal Lamb 2 in. long. The letters have 

 the same signification as elsewhere, except N. Nasal capsules, u. b. t. Septum nariura. 

 L. Lacrynial. PI. Palatine. Eu. Arrow indicating the course of the Eustachian tube. 

 /. Incus, m. Malleus. M. Meckel's cartilage. H. Hyoid. Ps. Petrosal. T)-. 

 Tympanic. 



incus. In the bird the corresponding part enlarges, ossifies, and 

 becomes the os quadratum, retaining its primitive connexion with the 

 pterygoid. In the mammal, the proximal end of Meckel's cartilage 

 ossifies and becomes the malleus, while the rest ultimately disappears. 

 The ossific mass which is formed around Meckel's cartilage remains 

 quite distinct from the proximal end of that cartilage, or the malleus, 

 gradually acquires the form of the ramus of the lower jaw, and 

 eventually developes a condyle which comes into contact and articu- 

 lates with, the squamosal. In the bird, on the contrary, the ramus 



