4(36 MR HAROLD AXEL HAIG ON 



small elevations or " cristae" project into the lumen, and are lined by a much higher 

 type of epithelium than that found in the canals ; but as yet there is no evidence of 

 hair-like structures upon the free internal borders of the component cells. 



The cochlea is rather more advanced in development than would be the case in a 

 three-months human foetus ; according to KRATJSE,* the organ of Corti in the human 

 foetus at birth shows that the membrana tectoria is only commencing to form, whilst 

 the sensory epithelium lying upon the basilar membrane shows only a larger and a 

 smaller group of columnar cells. The author's preparations of the cochlea of a three- 

 months human foetus show the sensory epithelium as a group of columnar cells higher 

 than the remainder in the tube, but no sign of the membrana tectoria. The scala 

 tympani is present, but no membrane of Reissner as yet divides the upper cavity into 

 scalee media and vestibuli, whilst the rudiments of the spiral ganglion and cochlear 

 nerve are certainly to be made out, but are not at all advanced. 



In the Seal embryo under discussion, all three scalse are present, the spiral ganglion 

 is a marked feature, the membrane of Reissner is well defined, and the epithelium of 

 the organ of Corti is becoming differentiated, the component cells being higher upon 

 the outer side, and their free borders showing a well-defined clear zone. 



(x.) The pituitary body (see text-fig. 3). A specimen of the pituitary gland of 

 an adult Weddell Seal (Leptonycliotes weddetti) was examined histologically by 

 the author some time since, t and found to possess all three portions, viz. pars anterior, 

 pars intermedia, and pars nervosa, highly differentiated. The Sea-Leopard Seal in its 

 earlier phases of development possesses a very interesting hypophysis, which more- 

 over sheds some light upon the origin of the pars intermedia. Although a complete 

 account of the histogenesis of this structure is not possible in the present instance, 

 there are certain points in its development which are worthy of somewhat detailed 

 description, and for purposes of comparison the developing hypophyses of the rabbit 

 (at the twelfth, fourteenth, and nineteenth days) and of the three-mouths human 

 foetus were submitted to microscopical examination. 



A nearly median sagittal section taken through the pituitary of this Seal embryo 

 (the gland being in situ in the sella turcica of the ossifying sphenoid bone) shows the 

 following features : 



(i.) The anterior lobe (pars anterior), consisting of irregular columns of rather 

 large polyhedral cells, separated by wide blood-channels, the latter possess- 

 ing a well-marked endothelial lining ; at the posterior extremity of the lobe 

 the blood-channels are observed to open into large venous tributaries, which 

 ultimately join up and communicate with the cavernous sinus, the latter 

 being seen in section lying just anterior to the dorsum sellae of the sphenoid 

 bone (fig. 3, g). 



* See HERTWIG, up. cit. 



t Trans. Kaij. ,SV. Kilin., vol. xlviii. part iv., No. 31, 1913. 



(ROY. soc. EDIN. TRANS., VOL. L., -244.) 



