_Muscular Apparatus of the Head._--Figs. 9 and 10, 11 and 12 show the arrangement of the principal muscles that work the jaws and glandular organs in _Vipera russellii_ and _Naja tripudians_, which respectively represent the most formidable types of _Viperidæ_ and venomous _Colubridæ_. It is not necessary to give a detailed description of each of these muscles. Let it suffice to point out that all contribute in giving the greatest elasticity to the jaws, and at the same time strength sufficient to retain the prey and to cause it to pass from front to rear towards the œsophagus, by a series of alternate antero-posterior movements and analogous lateral ones. By means of these movements, which are participated in by the upper and lower maxillary bones, the palatines, mandibles or inter-maxillaries, and the pterygoids, the animal in a manner _draws itself_ over its prey _like a glove_, since the arrangement of its dentition does not admit of _mastication_. [Illustration: A A, Fascia covering the anterior and posterior temporal muscles; B, small gland; C, tendinous insertion of the fascia; D, poison-duct; E, poison-fang; F, reserve fangs; G, mandible; H, ectopterygoid muscle; J, poison-gland covered by the masseter; K, masseter inserted in the mandible; L, insertion of the temporal muscle; M, digastric muscle. A A, Ectopterygoid muscle; B, præ-spheno-pterygoid muscle; C, intermandibular muscle; D, præ-spheno-palatine muscle; E præ-spheno-vomerine muscle; F, capsule of mucous membrane surrounding the fangs; G, long muscle of the neck. FIGS. 9 AND 10.--MUSCULAR APPARATUS AND POISON-GLAND OF _Vipera russellii_ (_Viperidæ_). (After Sir Joseph Fayrer.)] [Illustration: A, Tracheo·mastoid muscle; B B, digastric muscle; C C, posterior temporal muscle; D D, anterior temporal muscle; E E, masseter; F, poison-gland, covered by the masseter and fascia; G, poison-duct; H, maxillary bone; I, neuro-mandibular muscle; J, costo-mandibular muscle. A, Entopterygoid muscle; B, poison-gland; C, poison-duct; D, poison-fangs; E, præ-spheno-palatine muscle; F, præ-spheno-vomerine muscle; G, capsule of mucous membrane surrounding the fangs; H, præ-spheno-pterygoid muscle (which erects the fangs); J, inter-mandibular muscle; K, ectopterygoid muscle; L, long muscle of the neck (_longus colli_). FIGS. 11 AND 12.--MUSCULAR APPARATUS AND POISON-GLAND OF _Naja tripudians_ (_Colubridæ_). (After Sir Joseph Fayrer.)] [Illustration: FIG. 13.--ARRANGEMENT OF THE SCALES OF THE HEAD IN ONE OF THE NON-POISONOUS _Colubridæ_ (_Ptyas mucosus_). (After Sir Joseph Fayrer.) A, Rostral scale; B, anterior frontals; B^1, posterior frontals; C, vertical; D, occipitals; E, supra-ciliaries; F, temporals; L, M, nasals; N, loreals, or frenals; O, anterior oculars, or præ-orbitals; P, posterior oculars, or post-orbitals; Q, supralabials; G, median infralabial; H H, lateral infralabials; I K, mentals.]