IVRI Anatomy
A free veterinary anatomy learning platform for B.V.Sc., M.V.Sc., DVM and veterinary medicine students worldwide, developed at the Veterinary Anatomy Section, ICAR-Indian Veterinary Research Institute, Bareilly—covering VCI/MSVE and international university curricula through regional anatomy, histology, embryology, comparative biomechanics, clinical notes, quizzes and revision.
The sphenoid bone acts as the keystone of the cranial base, situated rostral to the occipital bone. In the ox, the sphenoid is terraced, meaning the rostral portion (presphenoid) sits at a higher elevation than the caudal portion (basisphenoid), reflecting the kyphosis of the cranial base.
Basisphenoid (Os basisphenoidale): The caudal segment. Its dorsal surface features the sella turcica (Turkish saddle), which houses the pituitary gland. The dorsum sellae in the ox is high and thick, creating a deep hypophyseal fossa compared to the horse. The wings (alae) spread laterally to articulate with the temporal bones, forming the oval foramen.
Presphenoid (Os praesphenoidale): The rostral segment. Its body is hollow, excavated by the sphenoidal sinus, which communicates with the nasal cavity through the ethmoid meatus. The wings of the presphenoid form the caudal orbital wall and contain the optic canals.
Foramen Orbitorotundum: This is a pathognomonic feature of the ruminant skull. In the ox, the foramen rotundum and the orbital fissure fuse to form a single, massive opening. This transmits Cranial Nerves III (Oculomotor), IV (Trochlear), VI (Abducent), and the ophthalmic (V1) and maxillary (V2) branches of the Trigeminal nerve.
Oval Foramen (Foramen ovale): A distinct foramen in the ox located in the wing of the basisphenoid, transmitting the mandibular nerve (CN V3). This is absent as a discrete foramen in the horse, where it is represented by a notch in the foramen lacerum.
Alar Canal: Absent in the ox. This means the maxillary artery courses on the surface of the pterygoid muscles rather than through a bony conduit, altering the approach for vascular ligation in this region compared to the horse.
| OX (BOS TAURUS) | Foramen Orbitorotundum present (massive fusion of rotundum + orbital fissure). Alar Canal absent. Foramen Ovale present (large, discrete). Deep sella turcica with prominent hypophyseal fossa. Extremely large sphenoid sinus. |
| HORSE (EQUUS CABALLUS) | Foramen Orbitorotundum present; similar to ruminants. Alar Canal present (transmits maxillary artery). Foramen Ovale present. Flat; shallow fossa. Communicates with ethmoid labyrinth. |
| DOG (CANIS LUPUS) | Orbital fissure and Foramen rotundum are separate (no fusion). Alar Canal present (transmits maxillary artery). Absent; replaced by large foramen lacerum. Distinct foramen ovale for CN V. Shallow; indistinct dorsum sellae. Communicates with palatine sinus. |
| PIG (SUS SCROFA) | Orbital fissure and Foramen rotundum are separate. Alar Canal present. Distinct foramen ovale present for CN V. Deep pituitary fossa. Often filled with marrow in small breeds. |
| FOWL (GALLUS DOMESTICUS) | Multiple separate foramina for cranial nerves (no fusion). Absent. Absent; replaced by incisura ovalis in foramen lacerum. Shallow; indistinct dorsum sellae. Absent; pneumatized by other systems. |
Explore the hidden mechanics of why structures are present, absent or modified across domestic and wildlife species—and how each anatomical design supports movement, function and clinical practice.
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