THE M.ANDIBULAll AND HYOID MUSCLES OE AlAMMAUS. 595 
'J'olypeutes (Lubosch), Brady pus tri dactyl us (Kostanecki) 
M anis pen tadacty la (F. H. E.), Avliereas in Clioloepus and 
]\Ianis Javanica (Scliulman)^ Dasypus sexcinctus 
(Kostanecki), Dasypus u ovein cincta, and Bradypus 
inarmoratus (F.H.E.) the muscle spreads into the soft palate, 
forming a tensor veli palatinid This secondary ingrowth 
remains in connection with the original pterygo-tympanicns, 
and may or may not have fibres takiiig origin from the ptery- 
goid bone. 
The condition present in the latter four Edentates hardly 
differs — as far as regards the proximal portion of the muscle 
— from that present in higher Mammals where the whole 
muscle, i.e. pterygo-tympanicus + its ingrowth into the 
soft palate, has generally been called the tensor veli palatini. 
Schulman was of opinion that the relations of the pterygo- 
spinosus s. tympanicus of Ornithorh 3 mchus indicated the 
existence of a movable (Mouotreme) pterygoid in Pro- 
mammalia. In Echidna, however, the pterygo-tympanicus 
arises from the (Mammalian) pterygoid in stage 50 (though 
subsequently atrophying) — an occurrence that suggests that 
the origin of the muscle in the adult Ornithorhynchus from 
the (Mouotreme) pterygoid is a secondary occurrence. 
Further, adoption of van Kampeids theory that the tympanic 
bone was, phylogeuetically, a covering bone for a jaw with an 
iucudo-meckelian joint, and so a movable structure, makes the 
theory improbable. 
Lubosch doubted the homology of the pterygoid bone in 
the Zeuarthra and Pholidota Avith that of other ]\Iammals, 
and suggested that it might be homologous Avith the Echidna 
pterygoid, or possibly the result of fusion of a Mammalian 
Avith an Echidna pterygoid. The early stages are not yet 
known, but in Dasypus nove mein eta (embryo 30 mm.) 
and Bradypus inarmoratus (embiyo 30 mm.) the relations 
of the pterygo-tympauicus muscle to that bone were identical 
with those in Dasyurus, and the bone, which shoAved no 
1 Schulman was the first to recognise the genetic relationship between 
the pterygo-tympanicus and the tensor veli palatini. 
