MOKPHOLO(iY(JF CKANIAL MUSCLES IX SO:\IE VEETEBRATES. 193 



are similar to those of Rana ; in Alytes the submaxillaris arises, 

 like the mandibnlo-labialis, from the inner aspect of Meckel's 

 cartilasre, so that the two muscles are much more continuous 

 than is the case in Rana, Bufo, and Pelobates. The con- 

 dition in 10 mm. larvre of Pelobates is similar to that of 

 12 mm. Iarv83 of Raua; in 13 mm. larvae the mandibulo- 

 labialis has spread additionally into the upper lip, the condition 

 described by Schultze. He states that the submentalis is 

 attached to the inner aspect of Meckel's cartilage, but up to 

 the stage of 30 mm. it is attached, as in Rana, Bufo, and Alytes, 

 to the inferior labial cartilages, as a vei'y minute transverse 

 muscle. 



At metamorphosis in Rana, the attachment to the skin of 

 the mandibulo-labialis is lost, and the muscle forms one sheet 

 with the submaxillaris.^ 



Observations on the development of the mandibular 

 muscles have been made by Reuter in pig-embryos, and 

 in regard to the tensor tympani by Futamura in human 

 embryos. Reuter stated that the mandibular muscles are 

 first visible in pig embryos measuring 16 mm. in " Nacken- 

 Steisslange"^ in the form of an inverted Y, the two limbs of 

 which lie on either side of the lower jaw. The temporal 

 develops from the upper limb, the masseter from the lower 

 exterual limb, and the two pterygoids from the lower internal 

 limb. Xo mention is made of the tensor tympani or the 

 palatine muscles. According to Futamura the tensor tympani 

 and tensor veli palatini form a '^ganz einheitlicheu Muskel " 

 in human embryos of seven weeks. This Anlage and the 

 levator veli palatini are developed about the branches of the 

 palatine nerves from a '' Muskelblastemgewebe" which 

 " deutlichen Zusammenhang niit dem tiefen Teil der Platys- 

 maaulage erkennen lasst." '' Die Nervenaste f'iir diese 



' Submaxillai-is of Ecker and Gaup. 



- This stage is an advanced one, as the figures show that the ossification 

 or the lower jaw has begun. The Anlage of the mandibular muscles 

 was quite evident in a j)ig embryo of 8 mm. crown-rump measurement, 

 from which Text-fitj. 98 was taken. 



