62 VENOMOUS SNAKES AND THE PHENOMENA OF THEIR VENOMS 
epithelia are identical with those of the supralabial glands, and the anterior 
part of the poison gland is called the accessory mucous gland. This assump- 
tion is supported by the observations that in the epithelia of the anterior part 
the nucleus is driven near the base of the epithelia, which are spherically 
swollen. Such appearance is never manifest in the posterior part treated by 
the same technique. The epithelia of the duct are cylindrical, yet their 
contents are not so clear and homogeneous, and stain by carmine solution. 
The arrangement and ramifications of the glandular tubules are described 
by Emery and are shown to be more complicated in the posterior than in the 
anterior part. Emery maintains the presence of ramification of the tubules 
in the posterior glandular part. In the anterior part there are glandular 
lobes, whose orifices open into the central secretory way in from five to six 
regular series. No lobes are found in the posterior part. From behind, a 
protrusion into the lumen of the secretory way is projected. This protrusion 
contains a collecting canal from the posterior glandular part and represents 
the continuation of their central substance. 
The structure of the poison gland of Vipera berus, Vipera aspis, and vari- 
ous European vipers has been well studied by Fontana, Rudolphi, Meckel, 
Joh. Miiller, Brandt, de Betta, A. B. Meyer, and Leydig. 
The poison gland lies in a fascia-like, pocket-like, extension of ligamen- 
tum zygomaticum. The main muscular coat of the gland is furnished by 
M. masseter, and certain of the fibers are also sent from M. temporalis. 
The tough, fibrous capsule divides the gland into many main lobes by send- 
ing several lamellar foldings within the glandular parenchyma. The tough 
cover of the poison gland consists of a firm connective tissue which resembles 
in its texture the ground structure of leather. Beneath this firm capsule the 
tissue becomes much looser and forms within it a lymphatic space. The con- 
nective-tissue framework of the gland retains the same soft, loose character 
described above, and the gland itself represents a tubular construction. 
The poison gland has a triangular form, the front angle of which is drawn 
into a secretory duct. The gland lies in a firm connective-tissue sheath and 
through this it is surrounded by muscles from almost all sides. It is so 
arranged that in every act of biting a compression of the gland, and the sub- 
sequent evacuation of the secretion from the poison fang, are brought about. 
The secretory duct consists of firm, thickly woven, circularly arranged, con- 
nective tissue, which contains no muscle fiber. The tough sheath of the 
poison gland transforms in the interior into a wide-meshed frame, which 
incloses numerous lymphatic spaces. Beyond this network numerous blades 
radiate internally and hold many glandular tubules together in groups so as 
finally to result in so-called granules. 
According to the degree of fulness of the secretion, the lumen of the tubules 
may be quite wide, or the walls may be in contact with each other. The 
epithelium of the poison gland is low and cylindrical. The protoplasma 
is more or less strongly granulated, and some coarse granules are seen. The 
nucleus lies somewhat apart from the base, but never near the apex. In the 
