592 
F. H. EDGEWOR'l'H. 
before it atrophies could not be determined owing to want 
of material. 
The ptery go-tympanicus s. tensor veli palatini is 
the middle one of the three into which the primitive medial 
muscle or muscle- Anlage separates. 
Its development could not be followed in Ornitho- 
rhynchus. In Echidna — stage 50, the earliest available — 
the pterygo-tympanicus arises from the (Mammalian) 
pterygoid bone and is inserted into Meckehs cartilage. The 
muscle subsequently disappears, being absent in the adult 
(Schulmann). 
In Dasyurns the pterygo-tympanicus arises from the 
pterygoid bone and is inserted into Meckebs cartilage, tliere 
being no stage in which, as a separate muscle, it arises from 
the ala temporalis. In later stages the distal end of the 
muscle loses its attachment to Meckebs cartilage and becomes 
connected with the persisting distal end of the tensor 
tympani. Insertion into the tympanic bone does not occur. 
At the same time the proximal end of the muscle — hitherto 
attached to the pterygoid bone — additionally gi-ows inwards 
in tke soft palate and forms an aponeurosis with the muscle 
of the opposite side. The pterygo-tympanicus thus becomes 
the tensor veli palatini. The same series of events occurs in 
D i d e 1 p h y s a u r i t a . 
In the rabbit the pterygo-tympanicus s. tensor veli palatini, 
when first visible as a separate muscle, lies on the medial side 
of the internal pterygoid. Its proximal end does not gain 
any attachment to the ala temporalis or pterygoid bone, but, 
later, grows inward in the soft palate round the hamulus. Its 
distal end becomes attached to the tympanic bone, but there 
is no antecedent stuge comparable to that of Echidna and 
Dasyurus in which it is inserted into Meckel’s cartilage. 
It also becomes attached to the persisting distal end of the 
tensor tympani. In the pig the process of development is 
abbreviated. The muscle, as in the rabbit, is first visible on 
the medial side of the internal pterjgoid; its proximal end 
does not gain any attachment to either the ala temporalis or 
