50 PEOF. G. B. HOWES AND MR. H. II. SWINNERTON ON THE 



anteriorly with the basal ethmoifl, united by their postero-internal extremities with 

 the parachordal ; and, what is more, they are serially disposed at all stages with the 

 visceral skeletal arches. 



Eecent investigation by the reconstruction method has led to the conclusion that 

 tlie developmental processes occurring in the skull of Man himself are not easily 

 reconcilable Avith those generally believed to be passed through by even that of certain 

 other mammals ^ 



As is well known, Salensky in 1878 described- in the embryo Sturgeon a distinct 

 cartilaginous centre for the lateral cranial wall ; and Stohr, in 1880, discovering that 

 the parachordal of Triton^ appears in two pieces, in 1882 showed'* the basal portion of 

 the chondrocranium of Rana to be complex, if not actually composed of three pairs 

 of distinct elements — trabeculae, " mesotic cartilages," and " occipital plates " (para- 

 chordals). Miss Piatt has later described in Necturus^ the dorsal part of the " crista 

 trabeculse " as paired, and instituted, on consultation with Sewertzoflf, a comparison 

 with the alisphenoidal cartilage originally described by him in Acanthias in 97^. 

 AVhile Peter, in the same year as Miss Piatt, recorded the formation in Ichthyophis ^ of 

 so-called " dorsal trabeculae." Most important of aU, however, is the full monograph 

 of Sewertzoff, which has appeared during the progress of oru* work, in which ^, bringing 

 the whole subject to a focus, he shows that in the Elasmobranch Acanthias the trabeculse 

 take an insignificant share in the formation of the lateral cranial wall, and that this is 

 mainly formed on either side from the above-mentioned distinct cartilages (termed by 

 him the alisphenoidal), the pair of which, uniting with the trabeculse, contribute what 

 he has termed the prochordal portion of the resulting chondrocranium. In his 

 memoir he meets the challenge that if this cartilage be of the importance he claims, it 

 should be more generally forthcoming, by showing reason for its being present in 

 Pristiurus, that W. K. Parker had seen it in the Salmon ^, and that other 

 observers, and more particularly Miss Piatt and Peter referred to above, had probably 

 done so in other chordate forms. In view of this and of the similarity in posterior 

 extension of the trabeculse along the parachordal in Acanthias and Sphenodon, and of 

 the relationships of the latter to our otosphenoidal plate (PI. III. fig. 1), we consider 

 tliat this may perhaps represent SewertzofFs alisphenoidal cartilage ^^. 



' Levi, G. : Archiv mikr. Anat. Bd. Iv. 1900, p. 407. 



- Salensky, W. : Zool. Anz. Bd. i. 1878, p. 289. 



' Stohr, Ph. : Zeitsehr. wiss. Zool. Bd. xxxiii. 1880, p. 477. 



•' Stohi-, Ph. : Ibid. Bd, xxxvi. 1882, p. 91. 



' Piatt, iliss Julia : Morph. Jahrb. Bd. xxv. 1897, p. 377. 



' Sewertzoff, A. : Anat. Anz. Bd. xiii. 1897, p. 413. 



' Peter, K. : Morph. Jahrb. Bd. xxv. 1898, p. 555. 



' Sewertzoff, A. : Kiipffer Festschrift, Jena, 1899, p. 281. 



» Parker, W. X. : Phil. Trans. 1883, p. 129, pi. v. 



^^ During the passage of this Memoir through the press, Sewertzoff has announced details concerning the 

 development of the skuU in the Gecko (Ascahabotes fascicularis) which fully supports this conclusion (c/. Anat. 

 Anz. Bot. xviii. p. 36, 1900). 



