The peculiarities of the masticator muscles in rodents

Abstract

Comparative research concerning masticatory musculature in squirrel, muskrat and rabbit, take into account the emphasizing and morphofunctional interpretation of the osteomuscular particularities involved in the prehension and mastication processes. The development of the coronoid process on the muskrat and squirrel demonstrates the growing of the force when raising the mandible by increasing the action force attached to the temporal muscle, with insertion on the coronoid process. In comparison with that, in the case of rabbits, both the coronoid process and the temporal muscle are reduced. From a philogenetic point of view, it has been found that the species that have the articular condyle lowered at or under the level of the dental tables (carnivores) present a greater pressure force between the dental tables. Analyzing this aspect of the rodents taken into discussion, we noticed the lowering of the articular condyle up to the inferior molars' plane, in the case of squirrels and muskrats, but through obliquity, namely through cranial caudal and dorsoventral movement. This peculiarity is emphasized through the analysis of the angle formed by the axis of the mandible recurved branch (passing through the mandibular condyle) with the axis of the horizontal branch of the mandible, where it was noticed that along with the increase in the angle formed by the two axes, which becomes an obtuse 160 degree angle on the squirrel and 130 degrees on the muskrat, there is also a lowering of the articular condyle up to the molar level, while in the case of carnivores, the lowering of the condyle is done without the modification of the angle between the two axes, which measures approximately 90 degrees.Keywords: squirrel, muskrat, rabbit, bone, muscle, skeleton RESUMO Investigações comparativas com respeito à musculatura mastigatória do esquilo, do rato-almiscarado e do coelho buscam o realçamento e a interpretação morfo-funcional das particularidades do sistema dos músculos esqueléticos envolvido no processo de agarramento e mastigação. O desenvolvimento do processo coronoide no rato-almiscarado e no esquilo demonstra o aumento da força no levantamento da mandíbula por meio do aumento do braço da força de ação do músculo temporal com inserção

Angioarchitectonics and Distribution of Common Carotid Artery Terminals in Domestic Rabbit

“…The transverse artery of the face is well developed and emits many masseteric branches in correlation with the development of the masseter muscle at this species (Spataru et al, 2013).…”

Comparative study of the digastric and the stylohyoid muscles between wild boars (Sus scrofa scrofa) and domestic swine (Sus scrofa domesticus): revisiting the gross anatomy

“…In humans, Madeira [12], Standring [24], and Khan and Bordoni [13] would claim the mastoid incisure of the temporal bone as being the point of muscle origin. In the domestic ruminants [1,11], equines [1,15,25], crabeating raccoon [16], red squirrel [21], black-eared opossum, moonrat, white-tailed deer, fox squirrel, and brown rat [17], the digastric muscle would pursue its path from its caudal belly, by means of a strong intermediate tendon, to have its continuity rostrally interrupted by the emergence of the rostral belly of the digastric muscle. Peculiarly in equines, the caudal belly would present the occipitomandibular part set laterally and inserted in the caudal edge of the angle of the mandible [1,15,25,26].…”

“…Spataru et al [ 21 ] whilst studying the red squirrel ( Sciurus vulgaris ), and Ferreira et al [ 22 ] whilst analyzing the black-capped capuchin ( Cebus apella ), have pointed out that the digastric muscle would originate in the paracondylar process of the occipital bone however, in the first species mentioned the origin would also involve the caudoventral region of the tympanic bulla. Yet, in rabbits, the anatomic region quoted by Muhl and Newton [ 23 ] has been the paramastoid process at the base of skull.…”

“…Spataru et al [ 21 ] described that, in the red squirrel, the attachment of the rostral belly of the digastric muscle would take place together with the mylohyoid and geniohyoid muscles upon the merger of the same in the intermandibular space. Yet, in the moonrat, the muscle insertion has been visualized on the ventrolateral surface of the mandible, ventralwise to the lower molars.…”

Estudio del cráneo mediante morfometría geométrica en dos especies de <em>Sylvilagus</em> Gray, 1867 (Mammalia: Lagomorpha)

“…Pero sí que aparecen diferencias entre las dos especies estudiadas, tanto de tamaño como de forma, presentando S. brasiliensis un cráneo de menor longitud que S. floridanus -algo lógico si se atiende al menor peso corporal y longitud corporal de esta última especie-, y siendo aquel más corto de cara y más ancho de bóveda. Al tratarse de estructuras no especialmente importantes de inserción muscular, ni albergar externamente estructuras funcionales (como podría ser todo lo relacionado con la vista) (Spataru et al, 2013;Watson et al, 2014), y vistos los requerimientos ecológicos similares para ambas especies estudiadas (Castañeda et al, 2015), este estudio sugiere que esta variación de la forma entre especies podría tratarse de un mero cambio derivado de la diferencia . Los hitos situados en la bóveda craneal (9, 10 y 11) fueron los que más diferencias presentaron entre especies.…”