1901.] XATUKAL SCIEXCE^ OF PHILADELPHIA, 231 



skeletal structures. Since it will be necessary hereafter in study- 

 ing the development of the Eustachian tube to take into consider- 

 ation the modifications undergone by the neighboring skeletal 

 parts, it may be well to point out these parts in the present stage. 

 The very dense segregated mass which may be seen in fig. 10 

 (3/. and Q.), immediately external to and beneath the pharynx, is 

 the Anlage of the cartilagiuous mandibular arch. That portion 

 of the arch which underlies the pharynx is the mandibular or 

 ^leckel's cartilage (M.), while that external to it is the quadrate 

 or suspensorium (Q-). In the figure there is no distinct separation 

 between these two portions, but more anteriorly the mandibular 

 Anlaxje can be seen to be separated from the quadrate b}'' a slight 

 space in which the mesenchyme cells are less densely aggregated 

 (fig. 11, M. — shown here owing to the oblique section, the left 

 side being cut more anteriorh'- than the right). In fig. 10 (i/. ) 

 only the most posterior part of the mandible can be seen. The 

 mandible, as in all anuran tadpoles, extends transversely beneath 

 the floor of the mouth. External to the lateral wall of the 

 pharynx (right side) is the quadrate cartilage ( Q.), which ven- 

 trally becomes continuous with the mandible and at the same point 

 sends upward and outward a strong process, the orbital process or 

 processus muscularis {Pr.M.) (Gaupp). This process with the 

 inner portion of the quadrate forms a deep concavity, underlying 

 tlie eye and containing the muscles of mastication. That portion 

 of tlie quadrate which lies in contact with the pharyngeal wall is 

 the palato-pterygoid process or commissura quadralo-cranialis ante- 

 rior of Gaupp (fig. 11, Pr.q.c.a.). At its dorsal extremity this 

 part approaches, but is still separated from, a patch of dense tissue 

 in immediate contact with the dorso-lateral border of the pharynx, 

 the Anlage of the trabecula cranii (Tr.). 



On the right side of fig. 11 (fourth section posterior to that of 

 fig. 10), the mandibular cartilage has been passed, and in its stead 

 we find a very slight aggregation of mesenchyme forming a portion 

 of the cartilaginous hyoid bar. The trabecula cranii of the same 

 side has become much less distinct, and in the third section follow- 

 ing (fig. 12) has ceased to be any longer distinguishable from the 

 surrounding mesenchyme. The trabecule cranii at present are 

 thus mai'ked out only in their more anterior portion. Of the 

 quadrate cartilage we have only the body with its processus mus- 



