258 SUMMARY OF CURRENT RESEARCHES RELATING TO 



found with double epiphyses. It seems plausible to regard this as 

 atavistic rather thau pathological. Even in mammals, some trace of 

 duplicity may be looked for. 



Development of Eye-muscles in Duck.* — H. Eex finds that the 

 cells of the walls of the head-cavity in the duck undergo progressive 

 differentiation, and finally become converted into a distinct almost 

 cubical epithelium. The epithelium of the anterior wall gradually 

 loses its epithelial character, and is converted into embryonic connec- 

 tive-tissue. This connective-tissue preserves for a long period its dis- 

 tinctive character, and does not fuse with the ontogenetically older 

 connective-tissue in its vicinity. Its ultimate fate is uncertain. The 

 epithelium of the posterior wall partly shares in the formation of the 

 muscles, and partly degenerates. The eye-muscles originate from the 

 epithelium of the lateral walls. The dorsal part of the posterior wall 

 takes part in the formation of the M. rectus superior, the ventral cir- 

 cumference of the cavity in that of the common rudiment of the rectus 

 inferior and the rectus internus. The obliquus inferior has an indepen- 

 dent origin, but its relation to the head-cavity can easily be made out. 

 The rectus superior has a distinctly epithelial origin, and arises later 

 than the recti inferior and internus ; the origin of the obliquus superior 

 was not clearly made out. The connective-tissue which arises from the 

 anterior wall of the head-cavity plays an important part in filling up 

 the degenerating head-cavity. 



Development of Skull in Falconidae. f — M. Chomjakoff has been 

 able to make some observations on the osteology of embryos and nest- 

 lings of Buteo vulpinus, Pernis apivorus, Astur palumbarius, Accipiter 

 risus, Milvus ater, and Circus cineraceus. He finds that nestlings of 

 Buteo vulpinus have a well-developed processus basipterygoidei, as the 

 more primitive Falconiformes have throughout life ; the process aborts 

 in the late stages of development. All the forms investigated have an 

 independent jugal, and in all the nestlings the lachrymal is firmly united 

 to the prefrontal, but the orbital and nasal cavities are incompletely 

 separated. There is a distinct superciliary bone. In Buteo, Milvus, 

 Astur, and Accipiter the skull is directly desmognathous, in Circus 

 cineraceus it is indirectly desmognathous, in C. seruginosus it is schizo- 

 gnathous throughout life, and in Pernis it is schizognathous in the young 

 bird and indirectly desmognathous in the adult. 



. Dentition of Hatteria. J ■ — H. Spencer Harrison has studied the 

 development and succession of the teeth in this form. He finds that the 

 first dentition consists of about thirty-six minute teeth, originating 

 immediately below the epidermis, labial to the dental lamina. They are 

 never functional, are shed before hatching, and resemble the first teeth 

 of some Selachians. The teeth which are developed on the dental 

 lamina, and which function during the early life of the animal, are 

 members of two dentitions (the second and the third), the later teeth 

 coming to alternate with the earlier teeth instead of displacing them. 

 Successional teeth appear first in the premaxillaa after hatching, and, 



* Arch. Mikr. Anat., lvii. (1901) pp. 229-71 (2 pis. and 2 figs.). 



t Anat. Anzeig., xix. (1901) pp. 135-40 (3 figs.). 



X Quart. Journ. Micr. Sci., xliv. (1901) pp. 161-213 (3 pis.). 



