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The Cephalic Veins and Sinuses of Reptiles 
Ow ReductionsorihersimismonitaliSm ee eee ete see 67 
cs Distensiony or ther sinusmvestibulie nasins. 45. 9ece scenes 68 
d. Distension of the sinus palatinus and smaller sinuses. 70 
e. Lymph movements caused by variation of blood-pres- 
sure in the cephalic veins and sinuses......... al 
f. Summary of events which occur during the operation 
OhuneEsiwel omechamismrs aire cet eich eines 72 
g. General remarks on the distension of the cephalic 
MeEINSHAndSINUSESPOr hes Sallilaner ese eee 73 
C. Significance of the swell mechanism in the head of Sauria. 75 
Cesemouliine mechanisms cerns Ge cen 75 
b. General characteristics of the moulting process....... 80 
c. Exuviation by means of blood-pressure............... 84 
II. Description of a swell mechanism in the head of Ophidia........ 87 
A. The musculus constrictor vene jugularis interne.......... 87 
Ba Distensionuol whe) vems anGesinuSesis cu. oltre eee ee 90 
C. Significance of the swell mechanism of the Ophidia........ 91 
III. Description of a swell mechanism in the head of Testudinata.... 93 
A. The musculus constrictor vene jugularis interne.......... 93 
2.2 Distension yor the velnsvandesimuSeSrecierrpetelaieiienere rien 95 
C. Significance of the swell mechanism of the Testudinata.... 97 
IV. Ontogeny of the blood sinuses of the reptilian head............. 97 
V. Distribution and phylogeny of the swell mechanism............. 99 
Wc @lorenh acs) eine noe ens 8 ere Emin Men ae a ta GlotiGcGad ls Sox 105 
Vili Summary Or PartvSeCOnd . sc ack cosmic CO eer Ato ae eee 108 
The cephalic veins of the Reptilia as a group have received compara- 
tively little attention from students of vertebrate anatomy. In case of 
the Sauria, Ophidia, and Testudinata the larger venous trunks have 
been described but no attempt has been made to work out their closer 
relations or to follow their tributaries. A more thorough study of this 
field is suggested especially by the fact that the head of lizards, snakes, 
and turtles contains large blood sinuses whose significance has not been 
explained in a satisfactory way. Weber, 77, concludes, from his study 
of the sinus orbitalis, that this sinus acts as a substitute for the cushion 
of fat behind the bulbus in other vertebrates. In view, however, of the 
general distribution of blood sinuses throughout the head, such an expla- 
nation is obviously inadequate. It has been suggested by Hay, 92, that 
Phrynosoma utilizes a sinus for the accumulation of blood which it 
ejects from the orbit, but we must also account for the existence of simi- 
lar sinuses in other forms which are not guilty of the blood-letting habit. 
The ejection of blood by Phrynosoma indicates the existence of a 
mechanism for producing extraordinary blood-pressure in the region of 
