■68 



Mr. F. A. Dixey. 



[Nov. 25, 



and the final stages marked by the invasion of the calcified cartilage 

 and its replacement by true bone are in these two phalanges never 

 reached at all.* [Note. — Another instance of arrested development in 

 the digit of the Proteus is afforded by the interphalangeal joint 

 represented in the same figure. The cartilage, with a slight alteration 

 in the size and relative number of its cells, is seen to be quite con- 

 tinuous between the heads of the two phalanges, nor does it exhibit 

 the least sign of an articular cavity. The movement allowed by such 

 a joint must be limited, but that some does take place is rendered 

 probable by the position of the tendons seen at et and ft. Specimens 

 of intramembranous ossification in the Proteus are remarkable as 

 showing with great distinctness the original deposition of bone in the 

 form of globules, after a manner strictly comparable with the growth 

 of dentine.] In the newt the ossification of the terminal phalanx pro- 

 ceeds in the same way as in the Proteus, and is arrested at the same 

 stage ; but the penultimate phalanx undergoes the osteoblastic inva- 

 sion, and is remodelled in true bone in the usual way.f 



The specimens from which the figures and descriptions were taken 

 were all hardened in strong spirit, most of them having been previously 

 decalcified in weak chromic or saturated picric acid. They were then 

 imbedded by the cacao-butter method and cut by hand or by Leiser's 

 microtome. The greater number were stained as sections with 

 magenta, but some were stained in bulk with logwood, carmine, or 

 both, before being subjected to the process of imbedding. The best 

 results were obtained by the employment of a freshly-prepared solution 

 of magenta in oil of cloves. 



DESCRIPTION OP PLATES. 



Figure 1. Section in the sagittal plane through the terminal phalanx of a digit in the 

 pes of a foetal cat 4 centims. long. Decalcified in chromic acid and 

 stained with magenta, c, the unaltered cartilage of the base of the 

 phalanx ; towards the tip the cells are seen to be assuming the form and 



# This condition resembles one that is liable to occur in the costal cartilages of 

 the mammalia, where a layer of membrane bone (in these cases subperichondrial) is 

 found enveloping a core of cartilage which may or may hot be calcified. 



f Dec. 9. — The uncertainty that prevails respecting the homologues of the limb- 

 elements in fishes, renders it difficult to say how far this class can be brought under 

 the rule above laid down for the higher vertebrates. In connexion with this sub- 

 ject, which is still under investigation, the following facts are noticeable : — (1.) That 

 in the limbs of all fishes which possess these appendages there is found at an early 

 stage a cartilaginous endoskeleton, which may persist as such, or undergo various 

 degrees of subsequent ossification. (2.) That to this set of elements is superadded 

 in many fishes a series of dermal deposits of bone (with or without lacunas) , the 

 local relation of which to the endoskeletal elements corresponds with that of the 

 subperiosteal bony growth to the terminal cartilaginous phalanx in the higher 

 vertebrates. 



