808 MR. J. B. PERRIN ON BALZNOPTERA RosTRATA. [ Dec. 6, 
the other, altogether precluded the possibility of such a membrane 
existing in these situations. The object of the laxity of the fibro- 
cartilage at the squamosal concavity was evidently to allow of the 
passage of a strong ligamentous band from the under surface of the 
cartilage to the depression in the squamosal, also to allow of the 
transmission of vessels. 
On the inner side the elastic fibro-cartilage projected beyond the 
squamosal, and was firmly attached to a strong zone or belt, of a 
more dense fibro-cartilaginous material, which surrounded the tym- 
panic bone, affording to them an efficient retentive as well as pro- 
tective nidus. On removing the articular mass, the tympanic zone 
could be well seen; it was broader on the inner than on the outer 
side of the ossicle, and broader behind than in front. In the former 
situation it measured 2} inches from before backwards; in the latter 
2 inches, whilst its width on the inner side was only one inch. In 
the centre of this nidus the oval under surface of the tympanic bone 
could be seen to the extent of two and a quarter inches, measured 
in its long axis, and one inch and three-quarters measured trans- 
versely. 
The superficial or circumferential fibres of the articular cartilage 
at the maxillary end were prolonged forwards on to the circum- 
ference of the mandibular condyle, forming a capsular-like belt of 
attachment, thereby materially adding to the fixity of the cartilage. 
‘The fibro-elastic cartilage was still further protected by a dense liga- 
mentous band which passed, from the squamosal to the maxillary 
condyle, along its under surface. Surrounding it was a dense mass 
of connective tissue, in which ramified an intricate plexiform net- 
work of vessels and nerves. Imbedded in this connective tissue, on 
the inner side, was a small wedge-shaped muscle, about 33 inches 
long, arising tendinous from the osseous ridge leading from the con- 
dyle to the inferior dental foramen. It was about half an inch wide, 
and terminated in a fascial expansion which was inserted into the 
fibro-cartilage upon its upper and inner side. The action of this 
muscle seems to have been to draw the articular mass forwards and 
inwards, thereby limiting the outward tendency it would otherwise 
have when the lower jaw was approximated to the upper, and also 
concentrating the cartilage in the axial line of the mandible during 
that movement. 
The cartilage weighed, when removed, 2 lbs. Its cireumference 
measured 173inches. Its maxillary extremity measured transversely 
4 inches, and 2? inches from above downwards. Its squamosal end 
measured 5 inches laterally, and 43 from above downwards. It 
presented the well-marked shape of the squamosal articular surface, 
namely concavo-convex, the concavity being situated antero-inter- 
nally, the convexity postero-externally. Its length was 43 inches. 
This articulation is a true amphiarthrosis, exactly analogous to 
that between the vertebral segments of the human subject, minus 
the pulp. 
The muscles of mastication were moderately well developed, being 
short, thick, and strong, and so closely approximated to the articular 
