Sixth Day.
Skeletal System (continued).
C. The Skull.
1. Remove the skin and other tissues from the top of the skull and observe the large fronto-parietals, nasals, supra-ethmoid, premaxillæ, maxillæ, squamosals, exoccipitals, and pro-otics. The quadrato-jugals are very inconspicuous. The extrastapedial plate of cartilage is well marked and the bony columella may be seen lying underneath it. The sides of the skull are ossified and may represent the orbitosphenoids and alisphenoids of higher types. The supra-occipital consists of a piece of cartilage.
Fig. 15.—Dorsal view of Skull of Xenopus and Rana.
[In the Frog there is no supra-ethmoid present, but a sphenethmoid closes the front of the cranial cavity. The sides of the skull are cartilaginous. A quadrato-jugal is well marked, but the quadrate consists of a piece of cartilage at the posterior end of the quadrato-jugal between the pterygoid and the squamosal. The lower jaw articulates with it. The columella is usually not well shown.]
Make a drawing of the dorsal side of the skull.
2. Remove the skin from the roof of the mouth and note the parasphenoid and single vomer, pterygoids, which are large and send leaf-like processes towards the middle line covering the Eustachian passages, squamosals, quadrates, basi-occipital, ex-occipitals, premaxillæ, and maxillæ. The orbitosphenoid and alisphenoid are well marked. There are no palatines present.