356 EGBERT J. TERRY 



mm. and older, being replaced by cartilage (Noordenbos). 

 Parker ('85) and Fischer ('01) had already shown continuous 

 cartilage in the region between basal plate and cochlear promi- 

 nence in Talpa embryos of later stages. Tarsius exhibits still 

 another phase of vacuity at the basicochlear junction, present- 

 ing an extensive slit separating the ear capsule and cranial floor 

 (Fischer, '05). In the adult cat, a fissure separates the pars 

 petrosa from the basi-occipital and it appears that in the adult 

 pig the foramen lacerum anterius and the foramen jugulare are 

 connected by a fissure median to the auditory bulla (Mead, 

 '08). The persistence of an original fissure, growing larger as 

 the cranium enlarges, is an interesting phenomenon calling for 

 further study. The posterior basicochlear fissure of Talpa is 

 one of several spaces which, as Noordenbos has shown, are de- 

 rived from the original space separating the independently arising 

 otic capsule from the basal and lateral parts of the chondro- 

 cranium. That part of the original space between the base of 

 the skull and the ear capsule is broken up by the later formation 

 of synchondroses, uniting the auditory capsule with the para- 

 chordal plate and with the basal region which later enters into 

 the sphenoid; and so there arise a canaHs caroticus, an anterior 

 basicochlear fissure and a posterior basicochlear fissure. The 

 observations on cat embryos, presented here, show that the 

 origin of the cartilaginous basal plate and otic capsule are in- 

 dependent and that the fissura basicochlearis posterior is derived 

 from the original space separating the parts. 



Foramen magnum. In Lacerta the dorsal boundary of the 

 foramen magnum is the tectum synoticum. Fischer ('03) found 

 the apparent foramen occipitale magnum of the Semnopithecus 

 embryo larger than the future real foramen magnum, the hinder 

 part of the former being closed by membrane. This author re- 

 marks on the probabihty of the membrana atlanto-occipitaUs in 

 part undergoing ossification. Bolk ('03) described this region 

 in human embryos, and applies the name incisura occipitalis 

 posterior to a httle space filled with membrane made secondarily 

 by the approximation of the dorsal extremities of the occipital 

 side walls in the formation of the foramen magnum. Between 



