DEVELOPMENT OF THE SKELETON OF THE TUATAEA. 47 



Gadow alone among recent investigators has carefully examined a series of indi- 

 viduals, and he records further details. Chief among these is the discovery ] that the 

 Huxleyean foramen may be reduced to the size of a pin-hole or absent (op. cit. p. 467) 

 facts which point to the conclusion that its condition is indicative of variation in 

 degree of extension of chondrification, especially when it is remembered that it 

 transmits nothing. 



Huxley described the head of the suprastapedial process (p. 397) as connected 

 with the parotic cartilage of the skull. Gadow, on the other hand, records in one 

 example a ligamentous attachment to this ; he remarks of another that " it does not 

 touch the cranium " (p. 468) ; and of a third he writes, the hyoid is continued 

 " along the anterior and lower margin of the extra-columellar cartilage, upwards to 

 the parotic corner, when it does not fuse with, although it directly touches, the 

 cranial cartilage." Sufficient this to show that the suprastapedial is in its ultimate 

 attachment variable. 



With these facts in mind, we were especially attentive to the extrastapedial region, 

 and concerning it the following : Examined at Stage S, and onwards to those stages 

 in which the adult condition is assumed, lateral longitudinal sections through the 

 quadrate (PI. V. figs. 13 & 14) show that bone to be unossified dorsally. It is seen to 

 be overlain by the squamosal (sq.), and when successive sections are followed outwards 

 the extrastapedial process (e.c.) is seen in the inner series to pass (PL IV. fig. 13) into 

 the suprastapedial (s.st.}. As the sections become external the suprastapedial is seen 

 to approach the head of the quadrate and eventually to fuse with it, as in fig. 14 

 (s.st.), which passes through the Huxleyean foramen. Sections more superficial, as 

 regarding the continuity of the parts, combine the appearance of these two figures. 

 Examination of the whole series and dissection alike reveals (cf. PL IV. figs. 7 & 9) 

 an absence of cartilaginous connection with the skull ; and in the denial of this we are 

 in agreement with Gadow. 



The foregoing observations would at first sight appear contradictory to Huxley's. 

 Examination of his fig. 4, however, reveals an error, in the fact that he has indicated 

 as the exoccipital the parotic process of the opisthotic, as is proved by his delinea- 

 tion of its articular extremity. Allowing for this correction, his " parotic cartilage " 

 can only represent the articular head of the quadrate ; and, if so, his description 

 amounts to that of a union between the suprastapedial and the quadrate, such as we 

 have described and have observed not only at Stage S but at T. And, as a con- 

 sequence of this, it follows that cartilaginous continuity between the suprastapedial 

 and the skull does not exist, and that the quadratic union applies to the adult as well 

 as to the young. Eesorting to the earlier stages, with a view of ascertaining whether 

 this union is or is not primary, we find in sections at Stage R that it does not 



1 Gadow, H.: Phil. Trans. 179 B, 1889, p. 468. 



